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Batteries discharged to a low voltage in a single phase Symmetra frame

Issue

Single phase Symmetra battery modules are discharged below 95 VDC and the system will only be able to operate in bypass.

Product Line

Symmetra Power Array
Symmetra RM
Symmetra LX

Environment

All serial numbers

Cause

There are two possible causes of this:

1.) If a battery module fails and enters thermal runaway state, the chargers are commanded off in order to cool the battery and prevent the situation from getting worse. Because the chargers turn off, it is important that this fault be addressed in a timely manner or the battery bus voltage may discharge to a voltage at which the power modules can no longer run online. When this happens, the only way to provide output power is to place the UPS into a bypass state.

2.) When battery modules are installed in a Symmetra frame, it must be connected to utility power and turned on so that the chargers are active . If the Symmetra is powered down for more than 72 hours with the batteries left installed in the frame, they will discharge to a voltage at which the power modules can no longer run online. When this happens, the only way to provide output power is to place the UPS into a bypass state. All Symmetra and Symmetra RM units ship with caution labels and documentation to warn the customer not to install the battery modules prematurely. Please note: Symmetra LX was designed with a total-power off feature that eliminates these situations. This specific cause only applies to Symmetra Power Array and Symmetra RM.

Resolution

The Symmetra will not be able to startup if the battery voltage drops below approximately 95 VDC. If this happens the customer will need a fresh battery (greater than ~95 VDC) in order to wake up the PFC circuitry within the Power Modules. Before inserting this fresh battery module, it is important to remove all discharged battery modules installed in the system (this includes any battery modules in connected XR frames). Failure to do so will cause the fresh battery module to equalize with the discharged battery modules and also become discharged.

Batteries that experience a deep discharge under 80VDC should never be recharged due to possible internal battery cell damage. If the discharged battery modules were above 60 VDC, they can be recharged. Once the system has fully charged the one fresh battery installed in the UPS, the discharged batteries can be installed in the system one at a time to be recharged. Ensure that the system is fully charged before inserting each additional battery module.